Electrically powered furnaces which are suitable for use in research laboratories have become popular for a wide variety of research and development applications. Often, these laboratory furnaces are required to reach very high temperatures in order to be useful for various ceramic and metallurgical applications such as crystal growth and sintering of metal and ceramic materials. While the exact furnace requirements vary widely with the specific application, there has been a general demand for furnaces which 1) are relatively lightweight and portable, 2) possess the maximum interior oven space relative to the furnace size, 3) are safe and easy to operate, and 4) require a minimum amount of power and energy for operation. At the same time, it is desirable that the furnaces have the capability of operating at temperatures of 1700.degree. C. or higher, and of reaching such temperatures within a minimal period of time.
The ability of research furnaces to reach very high temperatures within a minimal time period, and to maintain these temperatures using a minimum of energy and power, depends upon several factors including the size and shape of the furnace, the size and position of the door, how well the door fits, the amount of variation or "free play" in the position of the door, the type and amount of insulating material used in the furnace, and other design features which minimize the escape of heat during operation. Initially, many research furnaces used doors which opened in the front of the furnace, and significant efforts and innovations were directed toward minimizing the escape of heat from around the edges of the door. However, it has been known for some time now that furnaces which are loaded from the bottom, through a door opening in the bottom, are advantageous for heat retention due to the tendency of heat to rise.
Nevertheless, heat losses through the doors of bottom loading furnaces can still present a problem where the desired temperatures of the furnaces are high and the differences between the furnaces temperatures and the temperatures of the surrounding environment are large. Typically, a bottom loading furnace is mounted in an elevated position above a stand or platform. A mechanism is provided for opening the door to the furnace by lowering it to the platform, and for closing the door by lifting it to its position in the bottom of the furnace. This type of mechanism is generally known, and will be referred to hereinafter, as a "lifting mechanism".
The lifting mechanism should serve several purposes including lowering the door in a smooth, vibration-free fashion; raising the door into the same exact position every time; and maintaining the door in a tight fitting position, free of movement and play, during operation of the furnace. Due to the importance of the lifting mechanism in minimizing heat loss, much effort has been directed to developing lifting mechanisms which serve one or more of the foregoing objectives. To date, however, inefficiencies have remained in the operation of high temperature bottom loading research furnaces which have resulted in the use of larger than desired heating elements, larger than desired furnace sizes and weights, and larger than desired power and energy requirements.